Electrolytic preparation of manganese dioxide



Aug. 26, 1952 ox 2,608,531

ELECTROLYTIC PREPARATION OF MANGANESE DIOXIDE Filed Nov. 2, 1949 2 Sl-lEETS-SHEET 1 Re/afion f Currenf Efficiency To Pressure 02 Compac Tiny 0f T/fan/um Anode-s Am s/s fz 20 I00 /Z0 I40 I60 Vo/zaye-Carrenf Dena/f Re/af/bnsh/p For T/J Anodes INVENTOR Aug. 26, 1952 ox 2,608,531

ELECTROLYTIC PREPARATION OF MANGANESE DIOXIDE /0 a0. 5o a0 Patented Aug. 26, 1952 ELECTROLYTIC PREnAItA'rIonoFU MANGANESE DIOXIDE Abraham L. Fox, Washington, D. assignor 'to 9:":3

ReginaldS. Dean, Washington, D. C; v

' This invention relates to the electrolyticpreparationof manganese dioxide. It relates "particularly to improved anodestobe used in the production of manganese dioxide by electrolysis of solutions containing manganese sulphate and sulphuricacid. 1

It is well known in the art to produceelectrolytic manganese dioxidehaving valuable propertiesas a depolarizer forprimary cells and for other purposes by the electrolysis of solutions containing'about 50 grams per liter of manganese 'assulphate and 25 grams per liter of sulphuric acid. This electrolysis has been carried oncommercially using graphite anodes and either graphite ordead cathodes; This combination has been-open to ajconsiderable number of practical objections. 'Inor'der to obta'in current efficiency above 7 0% it'hasf been necessary to carry 'onthe electrolysis within a fairly limitedirange of acidity. "maintain'the temperature around 90 C. and to use a low current density, namely, fromlO to 20 amperes "pjersquare foot. The close control of these conditions'has been rendered necessarynot only by the efiect; ,of the mentionedjv'a'riables upon the quality fof the product but'be'cause' the graphite anodes deteriorate rapidly when'fhigher acidity or higher current densities are used. Other materials for anodes have been suggested, such as platinum andyarious alloys of lead and othe'rmetals. These anodes, however, 'haveall be'en unsatisfactory either because of costlorthe quality of "the product produced. It is the aim of "the present invention to provide an anode for the production of electrolytic manganese whichpermits a wider choicebf the other "variables, such as solution temperature, acidity and current density, without a deterioration of thequality of the manganese dioxide produced to any such extent as has been heretofore known in the art. t l I have found that'anodes may be formed principally'of titanium in accordance with my copending application, Serial No'. 109,061, filed August 6, 1949, whichgive excellent results. It is not satisfactory, however, to usefmass'iye titanium of either the ductile or castv'ariety. All such solid forms of titanium which I have tried are not satisfactory as anodesforthe deposition Toffmanganese dioxide. The voltage required for deposition on such anodes is prohibitively high and the current efficiency poor; I have found, however, that if the anode be fabricated from titanium'chips, entirely satisfactory results may be obtained.

It has'jlikewise been necessary to 'i claims. (c1. 204--83) 'I'prefertouse titanium 'chipswhich are made by the mechanical disintegration, such as cutting with a lathe tool of the product formed by the reaction of molten magnesium ontitaniumtetrachloride. The chips-made from such a reduction product are conveniently purifiedfrom-magnesium and magnesium chloride by leaching" with dilute hYdI'OOhIOIiCaOid. Such chips contain a certain amount of hydrogen which appears to be actually advantageous to the production of anodes for the practice of my invention.

Titaniumchips preparedfin the manner described and having a sieves'ize up to '35mesh-are compacted under 5 a suitable pressure and in -a suitable 'diefor the production of the-anodesoi my-inventionmThe pressure used for "the production of theseanodes has a definite relation ship -to the behavior of the electrolytic process in which they are-used. In Figured, I have, shown the relationship between pressureused to compact the titaniumchips and the current efficiency for several diiferent' current densities. In every case illustrated in-this figure the cell was operated at 90 Cw ItZwill'be seen'that,- in general, the lower the pressure used tocompact the chips into the anodeand, therefore, the more porous the anode, the better will be the current efiiciency at any particular current density. The low. limit for the pressureused to compact the chips into the anodeis, of course, determined by the. necessary mechanical strength of the anode and its tendency to disintegrate during the electrolysis. I haveifound that pressuresaszlow as 10 tons per square". inch givean anode with satisfactory properties in this respect. pressures may be .used with some sacrificeiin anode strength and life.: 1 1. l

.Lower The results given arefor the preferredform of titanium for my invention, "namely,- the chips made from the reduction product of titanium tetrachloride with magnesium, which chips have been subsequently leached with acid. Increased mechanical strength can be obtained in anodes formed in this way by sintering invacuum'ortin an inert atmosphere. Such increasein strength, however is accompanied by a decrease; in the valueof such anodes for my inventionl as. an example, I heat an anode made by compacting the titanium chips at20 tons per-square inchrto 800C. for one hour in vacuum.,.The resulting anode gives approximately the same result in the electrolytic cell as would be obtained had the chips been compressed at 50 or tons per square inch. 1

Titanium chips made in other ways can .be

used for the practice of my invention and titabody at a pressure of from to 50 tons per square inch.

4. Process as defined in claim 1, in which the anode consists essentially of particles of hydrogen-containing titanium, having a size not greater than mesh, compressed into a coherent body at a pressure of from 10 to tons per square inch.

5. Process as defined in claim 1, in which the anode is partially coated with a film of graphite.

6. Process as defined in claim 1, in which the electrolysis is carried out at a temperature between atmospheric and 100 C.

7. The method of claim 1, iurther characterized by the electrolysis being carried out at a current density of from 30 to amperes per square foot.

ABRAHAM L. FOX

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Clemens Aug. 5, 1947 OTHER REFERENCES Transactions of the Electrochemical Society, vol. '76 (1939), pages 401 to 425.

United States Department of Interior, Bureau of Mines, Bulletin 463, published 1946, pages 66 and 67.

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1. PROCESS OF PREPARING ELECTROLYTIC MANGANESE DIOXIDE HAVING GOOD DEPOLARIZING PROPERTIES IN A DRY CELL WHICH COMPRISES PASSING A UNIDIRECTIONAL CURRENT THROUGH AN ELECTROLYTE CONSISTING ESSENTIALLY OF WATER, MANGANESE SULPHATE AND SULPHURIC ACID FROM A METALLIC CONDUCTING CATHODE TO A POROUS ANODE CONSISTING ESSENTIALLY OF TITANIUM PARTICLES COMPACTED INTO A COHERENT BUT INCOMPLETELY CONSOLIDATED POROUS MASS HAVING A LARGE SURFACE AREA WHEREBY TO FORM A DEPOSIT OF ELECTROLYTIC MNO2 ON THE ANODE, AND SEPARATING THE DEPOSITED MNO2 FROM THE ANODE. 